Influenza, commonly referred to as the flu, is an infectious disease caused by RNA viruses of the family Orthomyxoviridae. Influenza or flu viruses infect birds and mammals. Three of the five genera of Orthomyxoviridae are influenza viruses: Influenza A, Influenza B and Influenza C. Of these, Influenza A is the most common.
Influenza is typically transmitted through the air in aerosols produced by coughs or sneezes and by direct contact with body fluids containing the virus or contaminated surfaces. Seasonal epidemics of influenza occur worldwide and result in hundreds of thousands of deaths annually. In some years, pandemics occur and cause millions of deaths. In addition, livestock, particularly poultry and swine, are also susceptible to annual epidemics and occasional pandemics which cause large numbers of animal deaths and monetary losses. The newly emerged Chinese avian influenza A (H7N9) virus is one subgroup among the larger group of H7 viruses (10). As of Jul. 4, 2013, there have been a total of 133 laboratory-confirmed cases and 43 people have died, indicating a very high mortality rate (32.3%
Structurally, influenza viruses are similar, having generally spherical or filamentous virus particles of about 80-120 nm made up of similar molecular component. A central core comprising viral proteins and viral RNA is covered by a viral envelope made up of two different glycoproteins and a lipid coat derived from the cell that the viral particle is produced in. Two additional different glycoproteins are anchored within the viral envelope and include portions which project outward on the surface. The H7N9 virus exhibits several genetic features of mammalian influenza viruses, including the specificity of their HA protein binding to mammalian cellular receptors; a deletion in NA stalk associated with increased virulence in mammals; and an important mutation in the PB2 protein that is essential for the efficient replication of avian viruses in mammalian species. The efficient transmission of H7N9 virus in ferrets suggested that human-to-human transmission of this virus might be possible under appropriate conditions. As a result, the emergence of the novel H7N9 has raised concerns about its pandemic potential, as well as that of related influenza viruses.
New synthetic DNA vaccines have emerged as an attractive approach against various infectious diseases and cancers. Conceptually, DNA vaccines have many useful attributes over traditional vaccination strategies, such as live-attenuated vaccines, protein/peptide-based vaccines. While DNA vaccines have been shown to be capable of eliciting balanced CD4+ and CD8+ T cell responses as well as humoral immune responses in small-animal models, their progress in the clinic historically has been hampered by difficulties in generating sufficiently potent T cell and humoral responses in humans. Until recently, the DNA platform has been used primarily in prime-boost strategies along with viral vectors and proteins, thus creating an inordinately long testing and development window for addressing emerging pandemics rapidly. In order to address the technical hurdles associated with weak vaccine-induced immunity, we have recently applied many synthetic DNA design strategies, including codon/RNA optimization, the addition of highly efficient immunoglobulin leader sequences, use of ‘centralized’ immunogens to broaden immunity and remove dependence on any individual viral sequence, new formulations combined with highly efficient DNA delivery methods such as in vivo electroporation (EP), to improve the induction of immune responses induced by DNA vaccines in small animals, macaques, and most importantly, in humans.
Accordingly, there remains a need for an immunogenic influenza consensus hemagglutinin protein, for nucleic acid constructs that encode such a protein and for compositions useful to induce immune responses in mammals that are broadly cross reactive against multiple strains of influenza. There remains a need for effective vaccines against influenza that are economical and effective across numerous influenza subtypes for treating individuals, including ability to cross protect against multiple strains of influenza.